Light emitting diode (LED) lamps have been developed to replace conventional incandescent or fluorescent lamps for reducing electrical and maintenance costs, and for increasing reliability. LED lamps consume less electrical energy than conventional lamps while exhibiting much longer lifetimes. Such LED lamps typically include a power supply and a plurality of LEDs mounted on a flat or curved surface.
One growing use of LED lamps is the replacement of incandescent light bulbs in traffic signal lamps. A common conventional traffic signal lamp is illustrated in FIGS. 1A and 1B, and includes a housing 1, a front door plate 2, a lens 3, a reflector 4 and an incandescent light bulb 5. Retainers 6 affix the lens 3 to the front door plate 2, which opens via hinges 7 to allow access to the interior of the housing 1. Light bulb 5 screws into threaded electrical socket 8, which is electrically attached to a terminal strip 9, which in turn receives its power from the traffic signal controller.
It is known to replace the incandescent light bulb 5 with an LED lamp, along with the lens 3 since the lens may be designed specifically for the output of an incandescent light bulb. In a conventional traffic signal lamp retrofit procedure, the lens 3, light bulb 5, reflector 4 and socket 8 are all removed, and an LED lamp module 10 is installed onto the front door plate 2 to replace lens 3, as illustrated in FIG. 2. Wires 11 from the LED lamp module are connected to the terminal strip 9. The lamp module 10 includes up to several hundred LEDs all mounted on a flat printed circuit board and are evenly distributed across the lens area.
The above mentioned retrofit method has several drawbacks. First, it is time consuming and labor intensive to remove the reflector and socket, and access the terminal strip with new wiring. Because traffic is usually blocked in order to access traffic lights, time is of the essence. Second, in order to safely disconnect the socket connector wires from the terminal strip, and connect new wires from the LED lamp module to the terminal strip, the power to the traffic signal must be temporarily turned off, which disrupts traffic flow through the intersection. Finally, once the retrofit is complete, it is not possible to put the original incandescent lamp back in the traffic signal lamp, for example, in case a spare LED lamp module is not available.
U.S. Pat. No. 6,268,801, which is incorporated herein by reference, discloses a method and apparatus for retro-fitting traffic signal lamps with LED modules, without having to remove the reflector 4 and socket connector 8, and without having to access the terminal strip with new wiring. The LED module disclosed in this patent includes a plurality of light emitting diodes evenly distributed on a flat PC board that is the size of lens 3, a power supply electrically connected to the plurality of light emitting diodes, and wires extending from the power supply that terminate in a threaded electrical connector compatible with the socket connector 8. The method of retrofitting the traffic signal lamp includes removing the lens from the front door plate, removing the threaded light bulb from the socket connector, affixing the LED lamp module to the front door plate, and connecting the threaded electrical connector of the LED lamp module to the socket connector. This retrofit procedure is simple, takes very little time and labor, and can be safely performed without turning power off to the traffic signal lamp. Typical traffic signal lamps have lenses that are 8 or 12 inches in diameter. As long as the outer rim of LED lamp module has a similar shape and diameter as the outer rim of the lens, then the same retainers that secured the lens in place onto the front door plate can be used to secure the LED lamp module in place. Thus, the LED lamp module preferably has a flange that is shaped and sized to match the outer rim of the lens that it replaces.
It is also well known in the art to make LED lamps by mounting a plurality of outwardly facing LEDs to a spherical lamp head, which terminates with a threaded electrical connector. Such an LED lamp simulates the light distribution of a standard light bulb, except the light is generated by the outwardly facing LEDs instead of an internal filament. This LED lamp can be easily substituted for a conventional traffic light bulb, but the intensity from such a lamp can be problematic. Not only is it difficult to mount enough LEDs on the spherical lamp head to produce the desired luminosity, but light emanating therefrom must still reflect off of the reflector, which can be optically lossy and degrade over time. The traffic light lens may also have to be replaced to produce the desired radiation pattern.
Recently, more efficient and higher power LEDs have been developed that reduce the number of LEDs which are necessary to meet signal lamp output intensity requirements (e.g. can be as few as 2 for some applications). For example, Dialight Corporation (of Farmingdale, N.J.) markets an LED module 12 (shown in FIG. 3) containing only eighteen high power LEDs 14, which provide as much light output as a conventional eighty to three hundred LED array on a twelve inch diameter circuit board. To provide an aesthetically acceptable appearance, the Dialight LED module has all eighteen LEDs 14 mounted together in a concentrated small cluster on the rear wall 15 of the module's housing 13. A planar Fresnel lens 16 and curved outer lens 17 are both mounted to the flange 18 that engages with the front door plate of the traffic signal lamp housing. The Fresnel lens 16 collimates the diverging light output from the high power LEDs to evenly illuminate the outer lens 17. Wires 19 extend from the LED module for connection to the traffic signal lamp's terminal strip.
In order to fully illuminate the Fresnel/outer lenses 16/17, the LEDs 14 must be placed a minimum distance D1 behind the Fresnel lens. For a 12 inch diameter module, even with the LEDs placed at the very rear of the module, the distance D2 between the front surface of the flange 18 and the rear wall 15 still exceeds approximately 109 mm (D2 for 8 inch diameter module exceeds approximately 102 mm). Moreover, since there is no room behind the LEDs for the module's power supply 20, the housing sidewall must extend laterally far enough to accommodate the module's power supply 20 so that it does not block the light emitted by the LEDs from reaching the lenses 16/17. Since most conventional 12 inch diameter traffic signal lamps have a depth of approximately 112 mm±2 mm (measured from the back surface of the door plate 2 to the bottom of reflector 4 or to the socket connector 8 should it protrude up from the reflector bottom) and most conventional 8 inch diameter traffic signal lamps have a depth of approximately 80 mm±2 mm, and a spherical or parabolic shape that is narrower than the profile of the Dialight lamps, the depth and shape of these lamps simply prevents it from fitting inside conventional traffic lamp reflectors. Thus, the installation of the Dialight lamp is cumbersome and time consuming because it requires removal of the existing traffic signal lamp reflector, electrical socket, and electrical connection to the terminal strip.
There is a need for a high power LED lamp and method for retrofitting conventional traffic signal lamps with reflectors.